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Riverbank Erosion Risk Assessment Under Impact of Climate Change on Ho Chi Minh City, Pham Ngoc

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This presentation is part of the ProSPER.Net Young Researchers' School 2017 ‘Water Security for Sustainable Development in a Changing Climate’.

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Riverbank Erosion Risk Assessment Under Impact of Climate Change on Ho Chi Minh City, Pham Ngoc

  1. 1. RIVERBANK EROSION RISK ASSESSMENT UNDER IMPACT OF CLIMATE CHANGE ON HOCHIMINH CITY Presenter: A/Prof. PHẠM NGỌC Organization: International University Quater 6, Linh Trung Ward, Thủ Đức District, Hochiminh City Phone: (08) 372 44270; Fax: (08) 37244271 Email: info@hcmiu.edu.vn Website: http://www.hcmiu.edu.vn/ Hochiminh City, 9 March 2017 1
  2. 2. CONTENTS: I. Introduction II. Research framework and methodologies III. Results and discussions IV.Conclusions and recommendations 2 Riverbank erosion risk assessment under impact of climate change on Hochiminh City
  3. 3. I. INTRODUCTION 3 - However, beside of benefits, many water- related disasters from river, including: river bank erosion. For example: Lower DongNai river basin; dense river network, with 975km of river for navigation, cary 145 Mil.tons of goods/year - 1997-2007: Economic loss caused by water related- disaster in HCMC is 202 Bill. VND (10 Mil.$), in which river bank erosion damage is 24.6 Mil. VND. - In 2009, 114 severe erosion positions were recorded in HCMC (City transportation Department) 1.1. Needs of study
  4. 4. Generally, Climate and Hydrologic regime of river are strong factors influencing bank erosion. Currently, they are dramatically changed 4 Does CC increase risk of river bank erosion? Observed max-rainfall intensity at Tan Son Hoa gauging station Observed water level at Phu An gauging station, loacted in Sai Gon River Riverbank erosion risk assessment under impact of climate change on Hochiminh City
  5. 5. 1.2. Objectives and studied areas a) Objectives: - To assess current situation, development of river bank erosion (RBE) in HCMC; - To identify main driving factors of RBE relevant to specific river reach; - To assess the risk of CC on RBE b) Study area: - Main rivers flowing through HCMC: 5 Riverbank erosion risk assessment under impact of climate change on Hochiminh City Saigon Dongnai Soairap Longtau Cầu Binh Phuoc Cầu Dong Nai Hiep Phuoc Port An Nghia Canal Cape of Red Light Cat Lai Ferry Station
  6. 6. 2. RESEARCH FRAMEWORK AND METHOLOGIES: RISK BASED APPROACH 6
  7. 7. Hazard VulnerabilityExposure Direct risk Disaster Risk Exposure Disaster Risk Exposure Reducing Risk & Increasing Resilience (or adaptation) Indirect Risk Definition: the probability (likely, ‘chance’) of harmful consequences, or expected losses/damage (injuries, property, livelihood, economic activity disrupted or environment damaged, deaths) resulting from interaction between natural or human-induced hazards and vulnerable exposure units. Hazard - Mitigation = Vulnerability Concept of risk assessment 7 Riverbank erosion risk assessment under impact of climate change on Hochiminh City
  8. 8. 8 Current situation assessment and main driving factor identification Collection of secondary data Field investigation and measurement Location and magnitude of erosion Water levels, discharges, TSS Questionnaire to Local communities Mike models (NAM, HD, ST) Fuzzy Logic (ArcGIS) Calibration & Verification Set up CC/SLR Scenarios Risk assessment and mapping Research frame work: A risk based approach Riverbank erosion risk assessment under impact of climate change on Hochiminh City
  9. 9. 9 3.1. Situation assessment of river bank erosion in HCMC and main driving factors - Recently, developmet of RBE in investigated rivers tends to more complex, no reduction recorded; eventhough there are many protection structures constructed (20 projects completed until 2011). For example: III. RESULTS AND DISCCUSION Sông Sài Gòn: number of erosion positions seem to be increased, and move to downstream (district 2) instead ot Thanh Da island in previous. Resons: human activities, such as: navigation, construction in protected river-corrodor, or un- suitable structures
  10. 10. Sai gon river Factors influencing erosion Flow Ship generated wave Sand minning Ship parking Human occupation Bình Phước - Bình Triệu bridge x x x x Bán đảo Thanh Đa x x x Cầu Sài Gòn đến mũi Đèn Đỏ x x x x 10 Dong Nai River Factors influencing erosion Flow Ship generated wave Sand minning Ship parking Human occupation Đồng Nai bridge to Ba Sang island x x x x x Ba Sang island Tắc juntion x x x x Tắc junction to Cát Lái ferry x x x x x Nha Be river Factors influencing erosion Flow Ship generated wave Sand minning Ship parking Human occupation Mũi Đèn Đỏ to Nhà Bè junction x x x x Ngã ba sông Nhà Bè đến cảng Hiệp Phước x x x x x Long Tau River Factors influencing erosion Flow Ship generated wave Sand minning Ship parking Human occupation Nhà Bè junction to Ông Kèo harber x x x Ông Kèo harber Tam Thôn Hiệp junction x x x x Tam Thôn Hiệp to Tắc An Nghĩai x x x - Natural cherateristic of river: weak foundation, breaded river... - Other social activities in upper river basin:  Forest destruction: can be improved but need to collabration among provices  Construction of reservoirs: Dau Tieng, Tri Anreservoirs trap sediment (about 2,65 Mil. M3/year in Dau tieng, VKHTLMN, 2013). Riverbank erosion risk assessment under impact of climate change on Hochiminh City
  11. 11. 11 Riverbank erosion risk assessment under impact of climate change on Hochiminh City 3.2. Impact of CC/SLR on hydrodynamic in river system NAM (rainfall- runnof modeling) Reservoir operation scenarios Downstream boundary conditions: SLR scenarios, 2012 Version MIKE 11-HD for scenarios Mike 21 HD/ST model Simulation and scenarios analysis Initial, boundary conditions River network, cross-sections Upper boundaries for 2D model Topo. data Hazard maps Initial parameters
  12. 12. SIMULATED DOMAIN FOR MIKE 21 MODEL Thủ Dầu Một Biên Hòa Thị Vải Vàm Cỏ Riverbank erosion risk assessment under impact of climate change on Hochiminh City
  13. 13. Division of Sub-basin of upstream region for NAM model MÔ HÌNH NAM Riverbank erosion risk assessment under impact of climate change on Hochiminh City
  14. 14. ĐA GIÁC THIESSEN Weighted factor for input of rainfall data MÔ HÌNH NAM Riverbank erosion risk assessment under impact of climate change on Hochiminh City
  15. 15. R2 = 0.816 KẾT QUẢ HIỆU CHỈNH CỦA MÔ HÌNH NAM Calibration results of discharge hydrograph at Dầu tiếng and Phước Hòa gauging station, from 01/01/1995 to 31/12/2005 Calibration results of discharge hydrograph at Trị An gauging station from 01/01/2013 to 31/12/2013 Riverbank erosion risk assessment under impact of climate change on Hochiminh City
  16. 16. HIỆU CHỈNH MÔ HÌNH ĐIỀU TIẾT HỒ CHỨA Observed and simulated discharge released from Trị An reservoir in 2013 Riverbank erosion risk assessment under impact of climate change on Hochiminh City
  17. 17. Observed and simulated discharge released from Dầu Tiếng reservoir , 1989 to 12/2005 HIỆU CHỈNH MÔ HÌNH ĐIỀU TIẾT HỒ CHỨA Riverbank erosion risk assessment under impact of climate change on Hochiminh City
  18. 18. Observed and simulated discharge released from Phước Hòa resevoir, in 2013 HIỆU CHỈNH MÔ HÌNH ĐIỀU TIẾT HỒ CHỨA Riverbank erosion risk assessment under impact of climate change on Hochiminh City
  19. 19. Simulated river network in MIKE 11 model MÔ HÌNH MIKE 11 Riverbank erosion risk assessment under impact of climate change on Hochiminh City
  20. 20. Calibration results of discharge and water level hydrograph at some gauging stations : (a) Phú Cường, (b) Phú An và (c) Nhà Bè, 20/9/2013 9:00 - 22/9/2013 9:00 (a) (b) (c) HIỆU CHỈNH MÔ HÌNH MIKE 11 Riverbank erosion risk assessment under impact of climate change on Hochiminh City
  21. 21. Verification results of discharge and water level hydrograph at some gauging stations(a) Phú Cường, (b) Phú An và (c) Nhà Bè từ 19/10/2013 9:00 - 21/10/2013 9:00 (a) (b) (c) HIỆU CHỈNH MÔ HÌNH MIKE 11 Riverbank erosion risk assessment under impact of climate change on Hochiminh City
  22. 22. Calibration and verification of Mike 21 – HD/ST VT1 VT2 VT3 VT4 Riverbank erosion risk assessment under impact of climate change on Hochiminh City
  23. 23. Discharge: 4 & 9/2015 at VT2 Water levels: 4 & 9/2015 at VT2 Riverbank erosion risk assessment under impact of climate change on Hochiminh City
  24. 24. 24 Calibration and verification for estuaries region (Can Gio biosphere) Kết quả so sánh mực nước tại trạm Đồng Tranh từ ngày 19/10 – 21/10/2013 Kết quả so sánh vận tốc tại trạm Đồng Tranh từ ngày 9/10 – 21/10/2013
  25. 25. 25 Các kịch bản tính toán SC1 Real hydrologic situation in 2013 SC 2 CC & SLR to 2020 SC 3 CC & SLR to 2030 SC 4 CC & SLR to 2050 SC 5 CC & SLR to 2070 SC 6 CC & SLR to 2100 SC 7 Release flood, P = 5% SC 8 Release flood, P = 1% Scenarios for simulation and analysis Riverbank erosion risk assessment under impact of climate change on Hochiminh City
  26. 26. SIMULATED RESULTS DURING RAINY SEASON IN 2013 , FOR EXAMPLE
  27. 27. Sài Gòn River – Thanh Da Island Vmax = 1.3 m/sVmax = 0.45 m/s Thanh Đa triều xuống Bán đảo Thanh Đa Vmax = 1 m/s Vmax = 1.2 m/s Vmax = 1.1 m/s
  28. 28. Vmax = 0.8 m/sVmax = 0.3 m/s Thanh Đa triều lên Bán đảo Thanh Đa Vmax = 0.64 m/s Vmax = 0.7 m/s Vmax = 0.65 m/s
  29. 29. Simulated results at 4 typical regions 29 Vị trí 1 2 3 4 5 Flood season Vmax, tidal withdraw (to the sea) ~ 1.1 ~ 1.2 ~ 1 ~ 1.3 ~ 0.45 Vmax, tidal rise up (to inland) ~ 0.65 ~ 0.7 ~ 0.64 ~ 0.8 ~ 0.3 1 3 2 4 5
  30. 30. SIMULATED RESULTS OF EROSION AND DEPOSITION IN RIVER IN 2013, FOR EXAMPLE
  31. 31. 6 MONTHS DURING DRY SEASON erosion - 0.2m erosion -0.16m erosion - 0.25m erosion -0.18m erosion - 0.12m
  32. 32. THANH ĐA 6 THÁNG MÙA MƯA erosion-0.44m erosion-0.35m erosion -0.5m erosion-0.4m erosion -0.2m
  33. 33. THANH ĐA SAU 1 NĂM erosion -0.66m erosion - 0.51m Xói -0.75m erosion - 0.58m erosion -0.32m
  34. 34. SIMULATED RESULTS CORRESPONDING TO CC/SLR SCENARIOS  Erosion situation is reducing  Example for SC6 (2100)
  35. 35. To 2100
  36. 36. Simulated results after 3 months in flood season Erosion 0.3 m erosion 0.13 m 2100 2013 To 2100: + Erosion reduced about 0.17m + Deposition increased to 0.06m, and deposited area also increased Deposition 0.06 m Deposition 0.08 m
  37. 37. SIMULATED RESULTS CORRESPONDING TO FLOOD RELEASE FROM RESEVOIR SCENARIOS
  38. 38. TĐ 1% TĐ 5% Vmax = 2.1m/s Vmax = 1.8 m/s Vmax = 0.5-0.6 m/s Vmax = 0.7-0.8 m/s Thanh Đa island Thanh Đa island In comparison with SC1- 2013  SC7: V increase ≈ 40%  SC8: V increase ≈ 60%
  39. 39. In summary of hydrodynamic part: • In comparison with current situation: CC/SLR not affect much on hydrodynamic condition in river system (lower discharge, higher water level); therefore, tendency or erosion is reduced but higher deposition. • However, flood release from 2 upstream reservoirs cause serious change of hydraulic situation in rivers: velocity higher from 40% to 70%. Riverbank erosion risk assessment under impact of climate change on Hochiminh City
  40. 40. 3.3. Risk assessment relevant to scenarios 40 Bank materials Bank protection Bank vegetation Hydraulic (v, H) Rainfall pattern Bank occupation Navigation FUZZY LOGIC Risk assessment and mapping GIS tool
  41. 41. 41 modules in river bank risk assessment Riverbank erosion risk assessment under impact of climate change on Hochiminh City
  42. 42. 42 Input parameter and rasterize them for modelling, example for Thanh Đa island
  43. 43. 43
  44. 44. Fuzzification of parameter 44 Human occupation
  45. 45. 45
  46. 46. 46
  47. 47. For example: Sai Gon river: Bình Phước bridge to Bình Triệu bridge
  48. 48. Risk level Leng of river bank (m) 2013 (current) CC/SLR scenarios Flood probability 2020 2030 2050 2070 2100 5% 1% Low 46,218 46,465 46,465 46,402 46,183 46,219 46,091 46,103 Moderate 50,329 14,931 14,058 12,146 9,085 11,738 12,913 11,323 High 441,609 552,701 550,683 545,183 548,106 540,699 441,160 422,597 Very high 225,712 164,903 166,021 172,463 172,472 176,898 213,924 223,215 Extream 42,347 20,939 21,514 21,065 18,314 20,994 89,616 102,195 0% 20% 40% 60% 80% 100% 2020 2030 2050 2070 2100 5% 1% Thấp Trung bình Cao Rất cao Cực kỳ cao General assessment
  49. 49. IV. CONCLUSIONS AND RECOMMENDATIONS 49 Riverbank erosion risk assessment under impact of climate change on Hochiminh City
  50. 50. Conclusions (1) River bank erosion in HCMC is not mitigated in comparision with previous data. Main reason now is human activities instead of natural factors (soft soils, river morphology…) (2) Integrated Fuzzy logic and traditional hydrodynamic modeling is reliable method for risk assessment because many qualitative and quantitative factors can be included. The model predicted that: • CC not affect much on hydrodynamic regime in river system; but • Flood water released from 2 upstream reservoirs make severe change of velocity in river (40% - 80% higher); therefore, potentially cause higher bank erosion. 50
  51. 51. Conclusions (con’t) • Under current situation, 56% length of river banks is at high risk level, 32% at high to very high; only 12% at safe (low to moderate level); • In relative comparison, it is found that CC make incensement of high risk area from 12% to 13%; meanwhile flood released from reservoirs increase from 6% to 8% areas at extreme risk level. Therefore, urgent need to protect these regions to cope with CC 51
  52. 52. Recommendations • Effect of sedimentation change on erosion shout be further studied. • When application of fuzzy logic, several key factors should be included, not consider all of them • Try to make membership function and fuzzy rules more realistic basing on quantitative relationship and expert consultancy. • Need to determine thresh hole level which trigger erosion of river bank (may be in Lab experiment). 52
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